Effects of environmental metal pollution on reproduction of a free-living resident songbird, the tree sparrow (Passer montanus)

Abstract

Anthropogenic metal pollution is known to adversely affect bird reproduction; however, few systematic studies are available on the effects of metal pollution on breeding performance and parental investment in a common resident songbird, the tree sparrow (Passer montanus). We conducted this study in two sites, a long-term heavy metal polluted site (Baiyin [BY]) and a relatively unpolluted site at approximately 110 km distance (Liujiaxia [LJX]), to assess the potential effects of environmental metal contamination on breeding parameters (clutch size, hatching success, fledging success, and growth of nestlings) and parental investment. The results showed smaller clutch size, lower fledging success, and differences in incubation behaviors of tree sparrows in BY than in LJX. Although there was no difference in parental body condition (residual body mass) between the two study sites, the parents responded differently with respect to reproduction due to varying metal levels in their habitats and bodies. Higher Cd levels in the primary feathers of females in BY were associated with lower clutch sizes. Parental investment including incubation duration and feeding rates showed no significant difference between the two sites during the incubation and nestling periods, but the frequencies of incubation visits were higher in BY. Parental behavior during the incubation period was also negatively affected by the parental Pb and Cd levels. Although the nestling growth patterns were relatively similar between the two sites, the nestlings were smaller, had lower body weight, and fledged later and fledging rate was also lower in BY than in LJX. Metal concentrations were higher in nestling organs and feces in BY. Taken together, metal pollution might adversely affect nestling growth condition. Our results suggest a negative response in the reproduction of tree sparrows to long-term environmental metal pollution.